Self-checking binaural audiometric apparatus and hearing aid simulator



.Fuy 18, 1967 D. W. FLYGSTAD SELF-CHECKING BINAURAL AUDIOMETHIC APPARATUS AND HEARING AID SIMULATOR 2 Sheets-ShawI l Filed Aug. 13, 1963 INVENTOR. en/v M FlySr/m OSfllLflQ AMM/Plak /Ias I 37/I/ I I I I I MIRP//O AVE FIE. .l/

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SELF-CHECKING BINAURAL AUDIOMETRIC APPARATUS AND HEARING AID SIMULATOR Filed Aug. l5, 1963 Fl' E'. .2B

United States Patent O 3,331,925 SELF-CHECKING BINAURAL AUDXOMET- REC APPARATUS AND HEARING AID SEMULATGR Dean W. Flygstad, Roseville, Minn., assignor to The Telex Corporation, Tulsa, Okla., a corporation of Delaware Filed Aug. 13, 1963, Ser. No. 301,831 3 Claims. (Cl. 179-1) This invention relates generally to the field of audiometry and is more particularly directed to an apparatus and method of operation thereof for binaurally testing the hearing capability of individuals afflicted with a hearing loss.

In the art of testing the hearing capabilities of individuals and the fitting of hearing aids, where necessary, it is desirable to have a portable, accurate, versatile and easy to operate machine so that laboratory facilities, instruments and highly trained operators will not be required while maintaining and achieving results comparable to the present day high standards obtainable only under such conditions.

It is therefore an object of this invention to provide an improved audiometer.

Another object of this invention is to provide an improved audiometer which may also be loperated as a hearing aid.

A still further object of my invention is to provide an improved audiometer which may be easily and completely tested without the use of elaborate external equipment for determining its initial calibration and suitability for performing its intended use.

Another object of my invention is to provide a simulator for demonstrating the operation of a hearing aid characterized through operati-on whereby the power output is reduced in accordance with signal gain.

A still further object of my invention is to provide a new and improved method of checking all of the components in a dual-channel binaural audiometer.

A still further object of my invention is to provide a new and improved portable and Versatile binaural audiometer.

These and other objects of my invention will become apparent from a consideration of the appended composite drawing in which FIGS. 1A and 1B show in schematic and block diagram form a complete illustration of a preferred embodiment of my invention.

Referring now to the drawings, a dual-channel binaural audiometer is shown with a first channel in block diagram form at the bottom of the composite drawing and a second channel in electrical schematic form at the top thereof. Briefly, the pair of channels each includes a pair of microphones 10 and 11, a pair of amplifiers 12 and 13, a pair of attenuators 14 and 15, a pair of volume unit sound output indicators 16 and 17 and a pair of receivers designated as right and left receivers 18 and 19, respectively, Which are suitably mounted on a headband indicated Iby reference numeral 115.

As stated above, each of the two channels is identical and each channel may be connected to the output of an audio-signal oscillator indicated generally by the reference numeral 20.

Oscillator 26 is comprised of a transistor 21, having the usual emitter, collector and base electrodes, that is interconnected in the manner described below to a plurality of capacitors, resistances and an inductance through a plurality of adjustable switching means 27, 28, 29 and 30, each of which is connected to a common driving means 38, which is in turn connected to a knob 26. The collector on transistor 21 is connected to a negative ter- 3,331,925 Patented July 18, 1967 ICC minal through a resistor 22 and the emitter thereof is directly connected to a positive terminal. The positive and negative terminals may be connected to a suitable source of direct current. The emitter electrode is connected to the base electrode through resistor 24 and the base electrode is connected to the collector electrode through resistor 23. The collector electrode is also connected to the plurality of capacitances associated with the stationary contacts on switch means 27. The emitter electrode is connected to the plurality of capacitors associated with the stationary contacts on switching means 28 and 29 and to the plurality of resistances connected to the stationary contacts on switching means 30. The base electrode on transistor 21 is connected to the movable contact on switch means 27 through inductor 31 and conductor 25 to the movable contact on switch means 29 through conductor 25 and conductor 37 and to the movable contact on switch means 30 through conductor 25, conductor 37 and resistor 32. The movable contact on switch means 2S is connected to the movable contact on switch means 27 through conductor 36. The output of oscillator 20 appears at conductor 33 which is connected to switch means 34 and 35 for connection to amplifiers 12 and 13, respectively. lt may thus be noted by those skilled in the art that oscillator 20 is of conventional construction and the values of components may easily be determined and selected to provide the desired range of audio-frequencies for any given application and it is contemplated that any conventional, stable oscillator may be utilized as a source -of audio test signal.

Amplifier 13 is comprised of three stages of amplification consisting of transistors 40, 60 and 68 each having base, emitter, and collector electrodes. Transistor 40 is shown with its emitter connected to a positive conductor 74 and its collector connected to negative conductor 75 through resistors 51 and 50. A capacitor 52 is connected between the junctions of resistors 50 and 51 and positive conductor 74. The collector electrode is also connected to the base electrode through resistor 49. The base electrode is connected to positive conductor 74 through resistor 41 and capacitor 42. A microphone 11 is connected to the base electrode through coupling capacitor 44 and to positive conductor 74 through switch means 45, shown adapted to be -connected to a further switch means through suitable conductors (not shown) as indicated by the symbols x-x. The base electrode is also connected to the junction between resistor 48 and diode 43 through switch means 46 and a coupling capacitor 47. Resistor 48 and diode 43- are connected between negative conductor and positive conductor 74 and comprise a source of masking noise which covers substantially the entire audiorange of frequencies. Diode 43 may be an RF diode which possesses the characteristic of generating a broad band noise signal when connected in the manner shown.

The collector electrode on transistor 60 is connected to negative conductor 75 through resistors 57 and 61. The emitter electrode is connected directly to a positive conductor 74 and the -base electrode is connected to positive conductor 74 through resistor 59 and to the collector electrode through resistor 58. The base electrode is also connected to the collector electrode on transistor 40 through coupling capacitor S6 and resistor 53 having switch means 54 connected in parallel therewith. Conductor 55 is connected at the junction of resistor 53 and coupling capacitor 56 and is in turn connected to switch means 35 on oscillator 2t). The junction between resistor 57 and resistor 61 is connected to positive conductor 74 through capacitor 62.

Transistor 63 is shown with its collector electrode connected to negative conductor 75 through resistor 67 and resistor 61, its emitter electrode directly connected t0 positive conduct-or 74 and its base electrode connected to positive conductor 74 through resistor 66. The base electrode is also `connected to thecollector electrode through resistor 65 and to the collector electrode on transistor 60 through resistor 64 and coupling capacitor 63. The values of components utilized in amplifier 13 may be easily determined by ,one skilled in the art and depend to a large extent'upon the types of transistors utilized.. It is desirable that a stable linear amplifier, as is consistent with vgood engineering practice, be utilized.

Attenuator 15 includes a knob 88 which is drivingly connected to position-the movable contacts on switch means. 73, 72 and 71 through suitable driving means 89. The stationary contacts on switch means 71 are connected to conductor 77 through suitable resistances and the stationary contacts on switch means 72 are similarly connected to positive conductori 74 through suitable resistances to form a voltage divider across the output of transistor 68. The collector electrode on transistor 68 is connected to conductor 77 through capacitor 79 and coupling capacitor 78. Capacitor 79 is selected from the a range of values which will tend to block the low frequency -components of signals at the output of amplifier 13 and may be shunted by closing normally open switch contact assembly 82 which is connected across capacitor 79 through conductors 8) and S1.y The movable c-ontacts on switch means 71 and 72 are directly connected and are in turn connected to the base electrodeon output transistor 100 through conductor 84, coupling capacitor 85, resistor 86, interruptingswitch 87 and conductor 90. The collector electrode on transistor 100 is connected to negative conductor 75 through conductor 102, left receiver 19 and conductor 1tl3. The emitter electrode on transistor 100 f is connected to positive conductor 74 through resistor 97,v having a capacitor 98 connected in parallel therewith, and the base electrode is connected intermediate positive conductor 74 and negative conductor 75 through resistors 96 and 99, respectively. A volume unit power output indicator 17 is connected in parallel with receiver 19 through conductors 104 and 105.

The collector electrode on transistor 1119i? vis also connected to the stationaryv contact on switch means 73 through conductor 76 and the various impedance means indicated von the drawing, and to the movable contact thereon through resistor 93 and conductor 91.*The movable contact on switching means 73 is also connected to negative conductor 75 through capacitor 92. The collector electrode is also connected to the base electrode on transistor 100 through capacitor 99, the lower set of contacts on double-pole single-throw switch means 83 and conductor 90. The stationary contact on the lower set of contacts on switch means S3 is directly connected to the movable contact on the upper set of contacts, the stationary contact thereof is Ifurther connected to the collector on transistor 68 through conductor 80.

The collector electrode on transistor 1d@ is further connected to switch contact assembly 113 through conductor 94 and the capacitor 1%. Switch contact assembly 113 is interconnected with switch contact assemblies 114 and 112 through suitable driving means in turn connected to a pushbutton therefor whereby the three switch contact assemblies form a triple-pole single-throw switch to be used for purposes to be described below. Contact assembly'112 is shown adapted to be connected to switch 45 at the left-hand end of the drawing as indicated by the reference Characters v x-x. The stationary contact on switch meansv 113 is connected to negative conductor 75 through diode 111 and resistor 111) and to the positive conductor 74`through diode 197. A capacitor 108 is connected intermediate the junction of resistor 11@ and diode 111 and positive conductor 74. A variable impedance means 109 and switch contact assembly 114 are connectedV in parallel'with capacitor 10S.

A suitable power supply means 101 adapted for connection to a source of alternating current (not shown) emphasize the higher frequency components of input sig-` nals to the attenuator while the range of adjustment of variable impedance y169 was such asto provide clipping of the output of transistor -at levels of minus l0, minus 20, and minus 30 db.

While the physical placement of the majority of the components utilized in my invention may be left to the discretion of the designer, it is desirable to place microphones 10 and 11 a predetermined distance apart to obtain the binaural characteristic useful in performing certain andiometric tests. It is anticipated that the coupling means indicated by reference numerals 132 ando133- may be permanently mounted upon microphones 11 and 11i, respectively, and are designed to provide suitableV matching between the receivers 18 and 19 and microphones 10 and 11 when utilizing thesel-checking features of my invention. Coupling means 132 and 133 mayy be comprised of, for example, rubber tubing or the like.

In order to assure the validity of any tests and demonstrations given with the apparatus with which my invention is concerned, the rst operation to be performed before any tests, or series of tests, is the self-checking of all of the components inthe apparatus without the necessity of utilizing any additional equipment. This is accomplished in the following mannenThe apparatus is energized by connecting the power supply 101 to a suitable source of alternatingy current which in turn provides a direct current potential across conductors 74 and 75 and across the indicated terminals on oscillator 20. Switch means 35 on oscillator 20 is closed and knob 25 is utilized to position switching means 27, 28, 29 and 3i) to predetermined positions to supply a pure audio-tone of predetermined frequency to amplifier 13 through conductor 55. Attenuator 15 is set to a predetermined position to provide a desired degree of attenuation of the signal applied thereto. Left receiver 19 is coupled to microphone 10 through coupling means 133 which is possessed of the desired resonance characteristics to effect the desired coupling of receiver 19 with microphone 10.' Switch means 45A, corresponding to switch means 45 on amplier 13, is closed, the attenuator 14 is set to a predetermined position for attenuating the signal and the output thereof is observed on volume unit power output indicaing the output on volume unit power output indicator 17 which, again, must correspond to a predetermined unit value.v A comparison of the observed unit values on indicators 16 and 17 will indicate by any ditference between the two values, that one or more of the components in the system is not operating satisfactorily. If the readings are the same, the audiometer vis in calibration and will provide accurate test results.

Once it has been determined that the ventire instrument is operating in a satisfactory manner, vvarious tests may be performed in determining a hearing loss of an indvidual in a quantitative sense and a qualitative analysis may be made to ensure proper tment of a hearing aid having the desired operating characteristics necessary to compensate for the hearing loss ofy the particular individual involved.

The first test is to determine the hearing loss, if any, of an individual and is carried out in the following manner. Assuming the instrument is energized, switch means 35 is closed and the threshold of hearing for the individual undergoing tests is determined by first applying the receivers 18 and 19 to the auditory canal and adjusting attenuator to provide a range of output in five db steps for each of the test frequencies utilized, here indicated as five. The remainder of the switches indicated on the top portion of the drawing are left in the positions shown. After the test for a left ear has been completed, the right ear may then be tested to determine the hearing loss, if any, and during such tests, switch means will be open and switching means 46 and 54 may be closed to provide a masking signal to the ear not under tests. The same procedure is then utilized with the identical equipment for the right receiver. During the hearing loss tests, contact assembly 82 is closed to shunt capacitor 79, and contact assembly 83 is left in the position shown in the drawing.

After performing the quantitative tests to determine the hearing loss profile of an individual, my invention may be utilized as a hearing aid to simulate the operation of a hearing aid and in particular one which is characterized by operation in which the power output capabilities are Varied simultaneously or in accordance with the gain. In this mode of operation triple-pole single-throw switch means, including contact assemblies 112, 113 and 114, is closed to connect microphone 11 to the input of amplifier 13 and to connect diodes 111 and 107 to the collector of transistor 100 through dapacitor 106 to provide a clipping or limiting of the output thereof. The level at which the limiting or clipping occurs may be determined by the adjustment of variable impedance 109. At this time a voice or other suitable sources of audio-signal may be applied to microphone 11 to demonstrate the capabilities of the above described hearing aid apparatus. It is also possible to vary the simulated response characteristics of such hearing aid apparatus by utilizing switch contact assemblies 82 and 83, In the position shown in the drawing, the low frequency end of the applied signal is deemphasized, when contact assembly 82 is closed a normal frequency response is obtained and when contact assembly 83 is closed, the high frequency end of the spectrum of the applied signal is de-emphasized. It may thus be appreciated that a qualitative observation of hearing aid apparatus may be utilized in determining the proper apparatus to be applied to the individual having a -hearing loss.

It may easily be seen upon a consideration of the principles of my invention and the above discussion that my invention comprises a dual-channel audiometer which is versatile, easy to operate, will simulate a hearing aid to provide a qualitative and quantitative analysis of the requirements of an individual afflicted with a hearing loss.

It is understood that suitable modifications may be made in the structure as disclosed, provided such modifications come within the spirit and scope of the appended claims. Having now therefore fully illustrated and described my invention, what I claim to be new and desire to protect by Letters Patent is:

1. The method of testing a dual-channel binaural audiometer which comprises the steps of applying an audiosignal to one channel, coupling the output thereof to the second channel, observing the magnitude of the output of the second channel, applying an audio-signal to the second channel, coupling the output thereof to the first channel, observing the magnitude of the output of the first channel, and comparing the magnitudes of the outputs of the first and second channels.

2. A self-Calibrating binaural audiometer comprising in combination; first and second signal amplifying and characterizing channels, each including a microphone amplifier means, signal attenuating means, sound output indicating means and a receiver; a source of audible signal; switching means alternately operable to connect said source of signal to the amplifier in said first channel and to connect the microphone to the amplifier in said second channel and to connect said source of signal to the amplifier in said second channel and to connect the microphone to the amplifier in said first channel; and coupling means alternately operable to connect the receivers to the microphones in said first and second channels whereby the condition of all of the elements of a binaural audiometer may be determined from the magnitudes of the outputs of both of said channels, said audiometer being in proper operating condition when the output of each of said channels are of predetermined equal magnitudes.

3. A self-checking binaural audiometer comprising in combination; first and second signal amplifying and characterizing channels, each of said channels including arnplifier means having a pair of input terminals for selective connection to sources of signal, signal attenuating means, sound output indicating means, and a receiver; a source of audio signal; first and second microphones including means for coupling said microphones to a receiver; means, including means connecting the input terminals on said first -channel to said source of audio signal, connecting the receiver on said first channel to said second microphone, and connecting said second microphone to the input terminals on said second channel, operable to connect said channels in series cascade relationship; and further means operable to connect said channels in opposite series cascade relationship whereby the indications on the sound output indicating means are of predetermined equal magnitude when all of the components of each of said channels are in suitable operating condition.

References Cited UNITED STATES PATENTS 1,710,170 4/ 1929 Latour 179-1 2,394,613 2/1946 Houlgate et al. 179-1.7 2,481,900 9/1949 Blok 179-1.7 2,753,397 7/ 1956 Zwislocki 179-1.7 3,073,900 1/ 1963 Victoreen 179-1.7 3,089,561 5/1963 Michael et al 1791.7 3,229,038 1/ 1966 Richter 179--1.3

KATHLEEN H. CLAFFY, Primary Examiner.

A. H, GESS, Assistant Examiner. 

2. A SELF-CALIBRATING BINAURAL AUDIOMETER COMPRISING IN COMBINATION; FIRST AND SECOND SIGNAL AMPLIFYING AND CHARACTERIZING CHANNELS, EACH INCLUDING A MICROPHONE AMPLIFIER MEANS, SIGNAL ATTENUATING MEANS, SOUND OUTPUT INDICATING MEANS AND A RECEIVER; A SOURCE OF AUDIBLE SIGNAL; SWITCHING MEANS ALTERNATELY OPERABLE TO CONNECT SAID SOURCE OF SIGNAL TO THE AMPLIFIER IN SAID FIRST CHANNEL AND TO CONNECT THE MICROPHONE TO THE AMPLIFIER IN SAID SECOND CHANNEL AND TO CONNECT SAID SOURCE OF SIGNAL TO THE AMPLIFIER IN SAID SECOND CHANNEL AND TO CONNECT THE MICROPHONE TO THE AMPLIFIER IN SAID FIRST CHANNEL; AND COUPLING MEANS ALTERNATELY OPERABLE TO CONNECT THE RECEIVERS TO THE MICROPHONES IN SAID FIRST AND SECOND CHANNELS WHEREBY THE CONDITION OF ALL OF THE ELEMENTS OF A BINAURAL AUDIOMETER MAY BE DETERMINED FROM THE MAGNITUDES OF THE OUTPUTS OF BOTH OF SAID CHANNELS, SAID AUDIOMETER BEING IN PROPER OPERATING CONDITION WHEN THE OUTPUT OF EACH OF SAID CHANNELS ARE OF PREDETERMINED EQUAL MAGNITUDES. 